Because they do not corrode, are lightweight and are easy to clean, unlike metal conveyor belts, plastic conveyor belts are used widely, especially in conveying food products. Modular plastic conveyor belts are made up of molded plastic modular links, or belt modules, that can be arranged side-by-side in rows of selectable width. A series of spaced apart link ends extending from each side of the modules include aligned apertures to accommodate a pivot rod. The link ends along one end of a row of modules are interconnected with the link ends of an adjacent row. A pivot rod journaled in the aligned apertures of the side-by-side and end-to-end connected modules forms a hinge between adjacent rows. Rows of belt modules are connected together to form an endless conveyor belt capable of articulating about a drive sprocket, and the modules are provided with recesses on the inner surfaces for engaging sprocket teeth.
The belt modules often are provided with a resilient surface, for example a rubber surface, in order to increase friction between the belt and the conveyed goods and thus avoid slipping of the goods. Providing the high friction surface gives rise to the problem of attaching the surface so that it is adequately retained on the module and does not loosen or fall off after repeated use. There have been many attempts at attaching the high friction conveying surface, which typically is an elastomeric or other high friction material, to the belt module, which typically is formed from a rigid plastic material.
One example of such attempts is mechanical retention of the material to the module such as by means of tongue and groove arrangements and fasteners as shown in U.S. Pat. Nos. 4,832,193 and 4,925,013. Another example is integrally molded resilient material such as thermoplastic rubber by co-molding it with the hard plastic module body and providing structures for retaining the rubber mechanically in the module body including channels as disclosed in U.S. Pat. No. 6,948,613 and rivet-like elements as shown in U.S. Pat. No. 5,439,097. A further example is co-molded rubber top modules with rubber recessed into the module and deformed projections that define undercuts to provide mechanical interconnection as described in U.S. Published Patent Application 2005/241,923. Another example is co-molded rubber top modules with rubber thermally bonded to the flat module surface without mechanical retention as shown in U.S. Pat. Nos. 5,361,893 and 5,507,383.
While all of the foregoing approaches have offered some improvements and are widely used, the problem of insufficient retaining of the high friction material such as rubber to the conveyor belt modules still remains. There is no fixing arrangement and method heretofore available which satisfies the objective of providing the best possible and highest available degree of attachment. This is particularly the case for application of rubber to modules made from polyacetal resin material. Due to its very good physical properties and strength, polyacetal is a very common material from which conveyor belt modules are made. However, adhesion of thermoplastic rubber molded to polyacetal is very low. Therefore, there is a definite need for further improvement in retaining high friction resilient material on hard plastic conveyor belt modules.